Aren’t our brains amazing?

How we tend to notice when a room is messy, but not when it's clean.
How a negative interaction with a loved one can amplify all their flaws.
When one small thing goes wrong in your day and you can't let it go and suddenly it feels like the whole day was terrible.

Our brains are constantly making predictions based on our concepts and past experience to interpret the pleasant and unpleasant sensations in our bodies. The feedback from the body (in the form of sensation) about how the physical systems are working is called interoception -- being aware of the internal world.

Those concepts and guesses are how we make sense of sensation so we know what caused the sensation and what to do about it. More intense sensations are used to make emotions; less intense sensations are used to make thoughts and beliefs.